1. Field of the Invention
The present invention relates to barrier-coated rubber closures for use as medical vial closures in the pharmaceutical industry, and to a method of making such closures.
2. Description of the Prior Art
Unprotected rubber closures for vials containing pharmaceutical agents give rise to a multitude of problems and complications. First, the rubber closures can deteriorate and allow bits of rubber to contaminate the pharmaceutical composition. This can be hastened by the particular type of pharmaceutical composition contained within the vial, since some such compositions can react with the rubber to further deteriorate the rubber closure.
Furthermore, the rubber will often contain stabilizers, conditioners, or other additives which can leach out of the rubber and into the pharmaceutical composition resulting in a contaminated pharmaceutical composition which may be ineffective or harmful to a patient.
In an attempt to circumvent such problems, rubber closures have been developed, in which the leg portion which protrudes into the pharmaceutical vial is fully coated with a barrier layer, such as a polytetrafluoroethylene compound, in order to insulate the rubber closure from direct contact with the pharmaceutical product contained in the vial. In this way, contamination of the pharmaceutical by the rubber stopper is prevented. One major draw-back of such fully coated structures is their inability to seal the pharmaceutical vial from outside gases including air. Fluorinated resins, such as polytetrafluoroethylene (PTFE) make excellent barrier layers, but their ability to seal is extremely poor. Accordingly, fully coated PTFE rubber closures are inadequate where the exclusion of air from the vial is necessary or desired. (This characteristic is also generally true of variants and modifications of polymers, some of which may include additives and/or copolymers.) These variants and modifications may provide, as compared to pure PTFE increased elongation or resiliency, superior barrier properties, and better adhesion or compatibility with the rubber compound used for the closure. As used herein, the term "PTFE" is intended to encompass all such variants and modifications.
In any event, because of the relatively poor sealing properties of PTFE, partially PTFE laminated rubber closures have been developed. Typically, one of two methods are used for making such partially laminated closures. In the first method, PTFE is introduced into a mold half. The PTFE is cut such that it extends partially up the sides of the mold half. Rubber compound is then introduced into the mold and the closure is formed. Since the PTFE extended only partially up the sides of the mold, it only partially covers the formed part. One problem with this type of molding, is that due to the properties of the PTFE, it generally does not adhere well to the mold half and therefore can get dislodged prior to forming the part. Accordingly, a large number of unacceptable closures are developed.
A second method for molding partially PTFE laminated closures is shown in U.S. Pat. No. 4,915,243 to Tatsumi et al. Briefly, the lower portion of the stopper is formed by compression molding a rubber sheet laminated with a PTFE material. The PTFE/rubber laminate is preformed as a sheet to be used as a raw material for this process. The lower portion of the closure is then formed, generally including only the legs of the closure.
Once molded, the pieces are cut apart and loaded into a second compression mold. The second process molds pure rubber compounds to the top portion of the rubber/PTFE laminate to produce a partially laminated rubber closure. In order to produce such a closure, the sheet of rubber or rubber/PTFE laminate must be compressed from a flat sheet into a series of closures or partial closures. Accordingly, since some of the deformation is elastic and the stresses placed on the sheet are radial, the closure precursor or finished closure may deform significantly upon removal from the mold. Accordingly, precision parts can not be efficiently produced.
Further, closures with long leg portions protruding into a vial cannot be produced since the PTFE cannot be drawn into a mold under such compression molding conditions. One problem with the closures produced by this process, as well as other partially laminated PTFE closures is that once the vials are filled and the closures are secured to the vials, but before an aluminum cap is applied, the closure, with its smooth, low friction PTFE barrier coating, can back-out of the vial due to vibration of the vials on the production line.